An engine/generator combination is generically referred to as a generator set. One specific application for a generator set is to provide backup power in the event that the main power service for a facility fails. When using such a system, the engine is started and the generator produces power over the power bus when there is an electrical failure. By providing power over the power bus, the facility will continue to have power despite the electrical failure.
In another application, the generator set is used to supplement the power on the power bus during periods of peak demand from the manufacturing plant or facility. Thus, in this application, the generator set will come on line and provide additional power to the power bus during periods of peak load. When connecting to the bus in this case, it is extremely important that the phase of the electrical power from the generator match the phase of the power on the power bus. In order to synchronize the two power supplies, a synchroscope is generally connected between the different phases of the power bus and the different corresponding phases of the generator output, and the synchroscope provides a display of the phase difference between the two power supplies (i.e., between the power bus and the generator output). The operator can then adjust the engine speed to modify the phase of the generator set output in an attempt to match the output phase of the generator with the phase of the power bus. When the two phases are within a predetermined tolerance of one another, the operator can connect the generator set to the power bus. Although the above synchronization process is described in terms of manually adjusting the engine speed and manually connecting the generator set to the power bus, there are known prior art systems that automatically synchronize the generator set output to the power bus and connect the generator set to the bus.
Likewise, these systems are sometimes constructed to be capable of sensing a power failure and automatically starting the generator set and connecting it to the power bus. Sometimes they are constructed to automatically discriminate between a live and a dead bus and to close the breaker without synchronizing when a dead bus is detected, which is often referred to as dead bus sensing.
Although there are prior art systems that automatically synchronize a generator set to the power bus and that are capable to some extent of dead bus sensing and automatically connecting a generator set to a dead bus, there are disadvantages associated with such systems. For example, low cost systems generally monitor only a single voltage input to determine whether the bus is dead. In those cases, a zero volt reading will cause the controller to conclude that the bus is dead and will connect the generator set to the bus. These systems are particularly susceptible to a single point of failure which may include a frayed sensor wire, failed sensor, or other failure causing a zero voltage reading which would then cause the controller to conclude that the bus is dead and connect the generator set to the bus without synchronizing. Connecting a generator set to a live bus in this manner without synchronization can result in damage to the generator set and the electrical system and should be avoided. Thus, it is important to attempt to reduce the chances of connecting the generator set improperly to a live bus.
Some higher cost systems monitor the voltage on all three phases of the power bus. However, these systems typically will require a greater number of analog input/output channels on the controller. Analog input/output channels add cost to the controller and it is preferable to reduce the number of such channels without reducing the functionality of the controller.
It would be preferable to have a system that reduced the likelihood of a single point of failure causing an engine generator set to connect to a live power bus without synchronizing. These and other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the detailed description in connection with the drawings and appended claims.